Reflected light did not appear
Make sure that you have the max bounces set adequately high to show full global illumination effects. There is a preset that you can activate as well. You may also have to increase the intensity of the light source and adjust the exposure. The distance, size or intensity of the light seems to be different in your first render, because the shadows are much crisper than in the second.



Plane with Principled BSDF (Specular 0.5, Roughness 0.5)


Plane with Principled BSDF (Specular 0.0, Roughness 0.5)